Summer was going so swell for Andrea Bargnani getting a fresh start with his trade to the Knicks and reporting to Team Italy’s training camp late last month in terrific shape. But now a respiratory infection that felled him three weeks ago has officially knocked him out of next month’s European Championships.

“I think he’s very very disappointed’’ Team Italy’s associate coach Mario Fioretti told The Post yesterday after Team Italy’s exhibition victory over Montenegro. “He spent one month before training camp getting in shape. He was ready with the right mental approach. Everything was set for him.’’

Bargnani had hoped to parlay his work with the Italian Team in the championships into a fast start when Knicks training camp opens Oct. 1. But he lasted 10 days and is back home in Rome downing high-grade antibiotics still unable to work out.

Bargnani was hospitalized for four days this month. Fioretti said team doctors didn’t think he could get in shape in time for the Sept. 4 opener in Slovenia.

Nobody knows how Bargnani caught the infection and Fioretti said they don’t believe it’s pneumonia.

“It’s crazy because its summer like he’s jinxed’’ Fioretti said.

The good news for the Knicks is Fioretti said he expects Bargnani to be on time for training camp. The Knicks play in Toronto against Bargnani’s former team twice in the preseason.

“I know he feels better so I can’t imagine him not being ready for October’’ Fioretti said.